The present invention relates to electric circuit breakers and, more particularly, to an electromagnetically operated straight line motion dual-break contactor of the enclosed arc chamber type.
Electromagnetically operated dual-break contactors are generally constructed such that an armature is operated by an electrically generated magnetic field to cause displacement of moveable contacts to either engage with or disengage from fixed contacts. Springs are commonly employed to return the armature and moveable contacts to their non-energized position.
Opening the contacts in such contactors usually results in an arc being formed between the moveable and fixed contacts, particularly in circuits where a relatively large direct current (DC) is being interrupted. The temperature of such electric arcs, varying between 6,000 and 20,000 degrees Kelvin, exceeds the melting temperature of known metals and will cause melting and vaporization of the surfaces of the contacts. Melting and vaporization of the contact surfaces produce pitting and other surface irregularities which may reduce the area of surface contact on closure and increase the likelihood of contact welding due to the smaller current carrying area.
Numerous features have been incorporated in contactors in efforts to minimize contact arcing with the intent being to extinguish the arc as rapidly as possible. Since an arc can be extinguished by either reducing the voltage which sustains it or by extending or dividing the arc so that the existing voltage is insufficient to sustain it, approaches to arc extinction have included arc chutes to divide and/or extend the arc and air and magnetic devices to "blow" the arc out by extension. While these approaches are useful in relatively large contactors, their application to smaller contactors has not always been practical. For example, a 100 ampere contactor for an electric truck or car must be relatively small unit in which it is impractical to use air or magnetic devices of sufficient strength to blow out a fault current arc or to use a bulky arc chute to extinguish such an arc. In addition, the small size of such contactors limits the maximum available contact separation to a magnitude insufficient for fault current arc extinction. Although magnetic blow-out coils are often used in smaller sized contactors, commercially available contactors do not meet the size requirements for an electric vehicle and yet have suitable fault current arc extinction capability to yield long contact life.
It is an object of the present invention to provide an improved electromagnetically operated dual-break electrical contactor.
It is another object of the present invention to provide an electromagnetically operated dual-break electrical contactor of relatively small size but with relatively large current interrupting capability.
It is a still further object of the present invention to provide an electromagnetically operated dual-break electrical contactor of relatively small size that will interrupt a fault current of several times its rated current capacity.
It is still another object of the present invention to provide an electromagnetically operated dual-break electrical contactor in which arcs occurring between the contacts are effectively directed away from the contact tips and into an arc cooling screen without using permanent magnets, magnetic coils, air blasts or arc chutes.